What Is The Hurricane Season?

Stretching from early summer into late fall, the hurricane season is a time when atmospheric conditions create an environment conducive to violent storms.

Beginning in early summer and lasting until late fall, the hurricane season is a time when atmospheric conditions can create violent and devastating storms that originate over water, but sometimes move onto land. During this time, temperature, wind, moisture and other factors converge in just the right way to create massive, spiraling storms that can obliterate nearly everything in their path.

When is the hurricane season?

The official dates for the Atlantic hurricane season are June 1 to November 30, with 97 percent of hurricanes occurring in this time frame. Hurricanes can and have occurred outside of these dates, but overall, most tropical storms occur during this six-month period. Globally, September sees the most storms and May the least, but activity varies from region to region. In the Atlantic basin, August through October, and especially early to mid-September, is the most active period, with 78 percent of the tropical storm days, 87 percent of the minor hurricane days and 96 percent of the major hurricane days developing then. In the Northeast Pacific basin, storm activity occurs during a wider time span, stretching from late May or early June until late October or early November. The activity usually peaks around late August or early September. In the Northwest Pacific basin, tropical storms occur throughout the year, with a noticeable drop in February and the first half of March. Most activity occurs from July to November, peaking in late August or early September. In the North Indian basin, storm activity peaks twice, in both May and November. However, tropical cyclones develop anytime between April and December, and the most severe storms are seen between April and June and between late September and early December. The Southwest Indian and Australian/Southeast Indian basins share similar storm seasons, beginning in late November or early December and ending in May. The season peaks twice, once in mid-January and again in mid-February or early March. In the Australian/Southwest Pacific basin, storm activity stretches from late October or early November to May, with a peak in late February or early March.

Hurricane seasons seem to occur in cycles, in which the intensity of activity varies greatly and large periods of time are significantly quieter than others. Between 1944 and 1969, for example, an average of 2.7 major hurricanes occurred each year, but between 1970 and 1994, activity decreased, averaging only about 1.5 major hurricanes a year. Activity increased again beginning in 1995, with an average of 3.55 hurricanes occurring each year from 1995 to 2003. It is speculated that long-term temperature changes in the Atlantic Ocean cause the differing intensity.



What causes the hurricane season?

Hurricanes, also called tropical cyclones, need warm ocean water to form, which is why activity is highest during the summer and fall seasons. Because ocean water warms and cools slowly, it is not yet warm enough in the spring to generate the necessary heat to fuel the storm. Once the summer heat warms the water, however, the heat is retained throughout the fall, accounting for the wide space of time in which hurricanes can and do occur.

Warm weather provides the unique combination of atmospheric factors needed to produce a tropical storm or hurricane. In general, storm development depends on three basic factors: a pre-existing weather disturbance with thunderstorms; warm ocean temperatures (of at least 80 degrees Fahrenheit) that extend about 150 feet; and light upper level winds that maintain a relatively consistent direction and speed throughout the depth of the atmosphere.

Pre-existing weather disturbances, the starting points for a tropical cyclone, usually develop off the coast of Africa about every three to four days, as tropical waves featuring areas of turbulent weather. Tropical cyclones can also develop from the tail ends of cold fronts or from upper-level lows, but they all need warmth to progress into a full-fledged storm. This warmth is only found during the summer and fall, and causes the evaporation of large amounts of water, creating humidity. As the weather disturbance enters the warm ocean waters, winds near the surface of the ocean merge with the disturbance's low-pressure area, and the warm water adds moisture and heat to the air, which rises. The moisture is condensed, releasing heat that provides even more energy to the developing storm. The storm becomes more organized, forming thunderstorms that can eventually strengthen and develop into what is known as a hurricane.

The dates for the hurricane season encompass the bulk of storm activity, but they are not the only times when hurricanes occur. Hurricanes can and do form outside of this timeframe, but it is during this period when weather conditions are the most favorable for creating a tropical storm. During these warm summer and fall months, atmospheric conditions combine in such a way that hurricanes have a better chance of occurring than anytime else.

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